Superheterodyne radio receiver



SUPERHETERODYNE RADIO RECEIVER Filed Feb. l5, 1950 alancmg m/sedanceCanlroL VoLLce 313 d INVENTOR. BERNHARDUS GERHARDUS DAMMERS BYM AGENTUnited States Patent SUPERHETEROD UNIL RADIO RECEIVER BernhardusGerhardus Dammers, Eindhoven, Netherlands, assigner to Hartford NationalBank and Trust Company, Hartford, Conn., as trustee Application February15, 1950, Serial N o. 148,728

Claims priority, application Netherlands February 16, 1949 ln suchcircuit-arrangements it has hithertoA been custornary to supply thesignal oscillations from the antenna or from a high-frequency amplifierto the third grid. ln this event, however, the conversion conductance iscomparatively low.

The principal object of the present invention is to provide in a simplemanner, in a circuit-arrangement as described in the preamble, manual orautomatic control means to vary the strength of theintermediate-frequency oscillations in the anode circuit, withoutappreciably affecting the oscillator, and ensuring a satisfactoryconversion conductance and signal-to-noise ratio.

Further object of the invention will appear from the followingdescription.

With frequency converting tubes it is known to prof vide means forcontrolling the strength of the intermediate-frequency oscillations. Useis generally made of the so-called pentagrid converter, in which thecathode, a control-grid and a grid having positive potential serve as anoscillator, the input signal oscillation being supplied to a secondcontrol-grid located outside the two grids and separated from them by ascreen-grid. In this event, the second control-grid may at the same timebe used as a control-grid. .The oscillator eiect in the tube issubstantially not affected by the control.

According to the present invention, in a circuit arrangement asdescribed in the preamble, both the signal oscillation and the localoscillation are supplied to the grid nearest the cathode. Between theanode and the cathode there is interposed the series-combination of animpedance, from which the intermediate-frequency oscillations arederived, and the feedback impedance. The junction of these impedances isconnected to the second central grid, which grid has a positivepotential withrespect to the cathode. A control voltage is applied tothe third grid. By coupling the junction of the impedances to the secondgrid, it is ensured that the current owing through the oscillatorsection of the tube is independent of the control-voltage so that avariation of the voltage applied to the third grid does not materiallyaffect the production of local oscillations. However, a control of theintensity of the intermediate frequency oscillations occurs in the anodecircuit, since the anode current depends, in large measure, upon thecontrol-voltage.

In the aforesaid mixing circuits, in which so-called additive mixing isused, excessive coupling generally occurs between the circuits acrosswhich the local oscillations appear and the antenna circuit, due towhich excessive 2,712,597 Patented July 5, 1.955

radiation of the local oscillations by the antenna usually occurs. Thisdisadvantage is obviated in a simple manner in the arrangement accordingto the invention. For this purpose, there is interposed between theanode and the cathode a series-combination of the impedance from whichthe intermediate-frequency oscillations are derived and a circuit tunedto the local oscillator frequency. The latter circuit is coupled to aninductance which is connected between grid and cathode. The terminal ofthis inductance remote from the grid is connected through an impedance,preferably the parallel-connection of a resistance and a condenser, to apoint of constant potential. The input signal is supplied to a point ofthe said inductance, preferably the central point.

As compared with the aforesaid pentagrid arrangement, the arrangementaccording to the present invention has the advantage that a tubecomprising only three grids is sucient.

1n order that the invention may be more clearly under-V stood andreadily carried into effect, it will now be described more fully withreference to the accompanying drawing, in which:

Figure l is a schematic diagram of a circuit-arrangement in accordancewith the invention,

Figure 2 is a schematic diagram of another circuit# arrangement inaccordance with the invention. Referring now to the drawing and moreparticularly to Fig. 1, there is shown a mixing circuit-arrangementaccording to the invention. in this figure, an inductance 1 in theantenna circuit is coupled with the inductance of a parallel resonantcircuit 2 which is tuned to the input signal frequency. From circuit 2the signal oscillations arel supplied, through a condenser 3, lters 4, 5and a tapped inductance 6, to a first control-grid 9 of a pentode tube7. Tube 7 also comprises a cathode 8, a screen grid 10, a suppressorgrid 11 and an anode 12. 'Ihe anode circuit comprises a parallelresonant circuit 15 which is tuned to the intermediate-frequency andcoupled with a circuit 16 which is also tuned to this frequency. Fromthelatter circuit the intermediate-frequency oscillations are taken andsupplied to an intermediate-frequency ampliiier (not shown). A parallelresonant circuit 17 tuned vto the local oscillation frequency isconnected between the circuit 15 and a positive terminal of a source ofsupply voltage. The inductance of the circuit 17 is coupled with theinductance 6, the center tap of which is connected to the filter 5.Filters 4 and 5 serve to isolate the antenna circuit 2 from theintermediate-frequency and the oscillator frequency circuits. The lowerend of the coil gijs grounded through a parallel-combination of acondenser 18 anda resistance 22.

The cathode 8 is grounded through a biasing-resistor 23 which issuitably by-passed by a capacitor 13. The screen grid 10 is connected,through a condenser 19, to the junction of resonant circuits 1S and 1.7.Screen grid 10 is also connected through a resistance 20 to a positiveterminal of the source of supply voltage. Resistance 20 may convenientlybe replaced by an inductor. A resistance 14, which serves as a leakageresistance for the first control-grid, is connected between the terminalof iilter 4 remote from ilter 5 and ground. VResistance 20 maybedispensed with if resistance 22 is provided. The suppressor grid 11serves as a control-grid and is connected for this purpose to a voltagesource (not shown) adapted to be controlled manually or automatically inaccordance with the signal strength. This voltage source may be, forinstance, a conventional A-V-C source.

The circuit-arrangement operates as follows: Owing to the couplingbetween resonant circuit 17 and coil 6, local oscillations are producedin the latter. These local oscillations are applied between the cathode8 and the rst control-grid 9 of the tube. The input oscillations fromthe antenna are supplied to a tap on coil 6 at which no localoscillation voltage is developed, so that substantially no localoscillation voltage appears across the antenna circuit. Isolation of theantenna circuit is further improved by lters 4 and 5. n

Application of a control voltage to grid 11 causes a variation of thecurrent distribution between anode 1 and screen grid l0. However, thisdoes not vaffect the production of local oscillations, since the screengrid is coupled through the condenser 19 to the oscillator circuit sothat current flowing through the oscillator circuit is independent ofcurrent distribution between the anode and screen grid. However, thisdoes not apply tothe intermediate-frequency oscillations across-thecircuit 15, and for thesean leective control may be obtained 'by varyingthe 'voltageV applied to suppressor grid 11.

The tapping point of coil 6 is so chosen that no local oscillations areVsupplied to the antenna circuit. This tapping point will, as a rule,have to be at the center of the coil andthe capacity of the condenserhave to be approximately equal to the capacity between the cathode andthe iirst control-grid of the tube. The resistance 22 will haverto beapproximately equal to the input resistance of the tube.

Fig. 2 shows a modiiied embodiment` of the invention, which diiers fromthe arrangement shown in Fig. l in that the oscillator circuit 17 isconnected between the cathode and ground. In this case, the screen `grid10 is directly connected to the positive terminal of the supply and animpedance 21 is connected between the lower `end of inductance 6 andground to balance lthe inductance 6 relatively to the antenna circuit insuch manner that the latter does not radiate local oscillations.

.-While I have described my invention in a specific Vuse thereof and inspecic embodiments, I do not'wish to Lbe limited thereto, for obviousmodiiications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

What I claim is:

1. A mixing circuit arrangement for mixing a rst wave and a second waveto produce an intermediate frequency wave, comprising an electrondischarge tube hav- Iingrin successive dispositions a cathode, a firstcontrol grid, avscreen grid, a secondV control grid and an anode, aiirst impedance network tuned to the frequency of said intermediatefrequency wave and coupled between said anode and said cathode,a secondimpedance network interposed between said first impedance network andsaid cathode, means to couple the end of said first impedance networkremote from said anode to said screen grid, means to couple said secondimpedance network to said irst control grid in regenerative relationshipat the frequency of said second wave, means to apply said first wave tosaid rst control grid, and means to apply a control voltage to saidsecond control grid to vary the current-dist tribution between saidscreen grid and said anode.

2. A mixing circuit arrangement for mixing a rst wave-and a second waveto produce an intermediate frequency wave, comprising an electrondischarge tube having in successive dispositions a cathode, a firstcontrol grid, a screen grid, a second control grid and an anode, a firstimpedance network tuned to the frequency of said intermediate frequencywave and coupled between said anode and said cathode, a second impedancenetwork tuned to the frequency of said second wave interposed 18 will ibetween said first impedance network and said cathode, means to couplethe end of said first impedance network remote from said anode to saidscreen grid, an inductive element inductively coupled to said secondimpedance network, means to couple said inductive element to said firstcontrol grid in regenerative relationship at the frek quency of saidsecond wave, means to apply Ysaid first wave to said first control grid,and means to apply a control voltage to said second control grid to varytheicurrent distribution between said screen grid and said anode.

3. A mixing circuit arrangement for mixing a rst wave and a second waveto produce an intermediate frequency wave, comprising an electrondischarge tube having a cathode, a first control grid, a screen grid, asecond control grid and an anode, a first impedance network tuned to thefrequency of said intermediate frequency wave and coupled between Vsaidanode and said cathode, a second impedance network tuned to thefrequency of said second wave interposed between said iirst impedancenetwork and said cathode, means to capacitively couple the end ofsaidlirst impedance network remote from said l anode to said screen grid, atapped inductive element inductively couplied to said second impedancenetwork and having one endv thereof coupled to said -irst control y gridto apply said secondwave to said control grid-iu positive `feed-backrelationship, a third impedance net- Ywork intercoupling the other endof said inductive ele-` ment and ground potential, means to apply saidVfirst wave to the tap on said inductive element, and means to apply acontrol voltage to said second control grid to vary the currentdistribution between said screen grid and said anode.

4. A mixing circuit arrangement for mixing a rst wave and a second waveto Lproduce an intermediate frequency wave lcomprising an electrondischarge tube having in successive disposition a cathode, a rst controlgrid,v

a-screen grid, a second control grid and an anode, a first impedancenetwork tuned to the frequency of said intermediate frequency wave andcoupled betweensaid anode and ground, a second impedance network tunedto the frequency of Ysaid second wave and connected between said cathodeand ground, means to connect the end'of said first impedance networkremote from said anode to said screen grid, a tapped inductive elementinductively coupled to said second Vimpedance network and having one endthereof connected to said first control grid in regenerativerelationship at the vfrequency of said second wave, a balancingimpedance` connecting the other end of said element to ground, means toapply said rst wave between the tap of. said element and ground, andmeans to apply a control voltage to said second control grid to vary thecurrent distribution between said screen grid and said anode. Y

.References Cited in theV le of this patent UNITED STATES PATENTSDammers Ian. 15, 1952

